This invention relates to semiconductor devices and, more particularly, to improved apparatus for mounting semiconductor device pellets and semiconductor assemblies employing the improved apparatus.
Semiconductor pellets are usually mounted with metal plates on one or both sides, the plates serving as a stress relief mechanism, a mechanical coupling system, heat and current spreaders or mechanical protection devices or any combination of the aforementioned functions. The plates are frequently substantially coextensive with the metallic contacts on the pellet. If the plates are smaller than the contacts, there may be insufficient current spreading to adequately utilize the entire conductive area of the semiconductor pellet and, furthermore, there may be inadequate thermal coupling to the pellet to effectively remove heat therefrom. If the plates are larger than the contact, the metal plate may overlie regions of the semiconductor pellet other than the region to which it is electrically coupled. Consequently, the chance of undesirable device breakdown is enhanced, and spurious, perhaps harmful, capacitances will be formed.
A problem that has developed in the use of these metal mounting plates stems from the fact that burrs are sometimes formed around the periphery thereof. The plates are generally stamped from large sheet stock, and a slightly dull die or apparatus out of adjustment may cause the burrs. Typically, the burrs will occur on only one side of the plate. If the burrs are adjacent the header to which the semiconductor pellet-metal plate laminate is to be mounted, the burrs may cause a spatial separation between the face of the metal plate and the header and thus prevent full contact of the plate and the header. Consequently, thermal coupling between the header and the pellet may be inadequate. Furthermore, the mechanical strength of the coupling will be diminished. If the burr is on the side adjacent the pellet, a potentially more serious problem can occur. If the metal plate is substantially the same size as the metallic contacts on the semiconductor pellet and, as is usual, the contact terminates prior to intersection with the periphery of the pellet, the burr rests on the surface of the semiconductive pellet. If pressure is applied during the process of bonding the plate and the pellet, the inordinately high pressure occurring under the burr can cause the brittle pellet to fracture and result in device failure.
Efforts to eliminate the burrs have resulted in a cost for the metal plates that is unacceptably high for many applications.
It is an object of this invention, therefore, to provide a metal mounting plate that overcomes the aforementioned disadvantages and to provide new semiconductor assemblies making use of the plate.